Activated carbon has been widely utilized for removing trihalomethane and residual chlorine in tap water. In recent years, heavy metal ion such as chromium, manganese, cadmium, lead and mercury dissolved in tap water in very low concentration, particularly lead, have been a problem. However, activated carbon alone has little effect on removing such heavy metal ions.
On the other hand, it has been known that aluminosilicate, typically exemplified by zeolite, exhibits ion exchange function in water and adsorbs heavy metals in water.
It has been hitherto proposed that a mixture of activated carbon and natural zeolite be used for treating tap water (Japanese Unexamined Patent Publication Sho 61-86985); however, natural zeolite has a low performance of removing heavy metals. In addition, many kinds of water purifiers have been proposed in which aluminosilicate-based inorganic ion exchanger (for example, zeolite) and activated carbon are combined (Japanese Unexamined Patent Publications Sho. 61-86985 and Hei. 08-132026); however, zeolite adsorbs not only heavy metals but also calcium ion and magnesium ion in tap water, so that water after being treated with such purifiers does not have so-called refreshing feeling in the throat and is not preferable for health.
Also, a method of mixing calcium (Ca) type zeolite, silver (Ag) type zeolite, hydrogen (H) type zeolite and activated carbon so as to be accommodated in a cartridge (Japanese Unexamined Patent Publication Hei. 06-47383) and a water-quality modifier employing Ca type natural zeolite, Ag type natural zeolite and H type natural zeolite (Japanese Unexamined Patent Publications Hei. 03-229690 and Hei. 07-148487) have been proposed; however, the degree of Ca substitution of Ca type zeolite, the using ratio of various substituted zeolites and the using ratio of them to activated carbon are not described therein, and the mere random mixing of the raw materials is not capable of producing delicious water. Additionally, natural zeolite exhibits low performance for removing heavy metals which does not last for a long period of time.
With regard to the modification of water quality, techniques that use Ca type zeolite to adjust the concentration of calcium ion in water are known; however, techniques that also adjust magnesium ion as the other important mineral component have not been known. In addition, techniques to remove heavy metals in water simultaneously while modifying water quality have not been previously known.